This invention relates to a torus type vacuum shell for a nuclear fusion device useful for a toridal fusion reactor of the Tokamak type, and more particularly to improvements in a vacuum shell thereof.
In the toroidal fusion reactor which confines a plasma electromagnetically, such plasma is produced with a vacuum shell evacuated into a high vacuum state.
The vacuum shell is formed into the torus type by the use of a non-magnetic metal material. The vacuum shell is provided with poloidal coils which are wound and arranged in the poloidal direction, and toroidal coils which are wound and arranged in the toroidal direction.
As the poloidal coils, there are horizontal field coils which form horizontal magnetic fields in order to effect the vertical control of the plasma produced within the vacuum shell, vertical field coils which form vertical magnetic fields in order to effect the horizontal control of the plasma, multipole field coils which control the plasma so that the plasma itself may become circular in cross section, primary coils which produce the plasma by rapidly changing currents flowing therethrough, and magnetic limiting coils which control the plasma so that the plasma may not come into contact with the inner wall of the shell.
As the toroidal coils, there are toroidal field coils which are wound and arranged in a manner to surround the circular cross section of the vacuum shell and which confine the plasma into the vacuum shell.
In order to enhance the efficiency of producing the plasma and the performance of confining it, the various coils mentioned above need be brought as close to the plasma generating space as possible.
It is therefore desirable that the wall of the vacuum shell is formed to be thin.
On the other hand, the wall need be thick enough to endure a high vacuum (usually, above 10.sup.-8 torr) at the running for the plasma generation.
More important is that the wall construction need also endure intense electromagnetic forces which are caused by the coils at the running. If the vacuum shell wall is deformed by such external forces, it will touch with the plasma and be fused, the vacuum will break off, and the coils will be damaged.
In this manner, in determining the thickness of the vacuum shell, the contrary functions of raising the plasma generating efficiency and enduring the external forces are required.